The present invention relates to a method of exterminating a noxious clustered creature such as cyanobacteria (mycrocystis) that are generated at ponds, lakes or marshes.
It is known that cyanobacteria grow at ponds, lakes or marshes, and sometimes propagate themselves in large quantities to damage environment, for instance, they kill a large number of fishes and shellfishes and pollute water. These cyanobacteria are one kind of a fresh water algae, and each individual is a globular unicellular organism with a diameter from 3 to 6 xcexcm. However, many unicellular organisms are close to each other and are sheathed by a viscous sheath so as to be a cluster with globular or substantially globular form.
A gas cyst in the cell functions as a float, and the cyanobacteria rise near the water surface and suspend there. Cyanobacteria have a chloroplast in their cell, and their suspending near the water surface allows them to receive sunlight to photosynthesize. As a result, cyanobacteria are able to maintain their life and propagate themselves.
As described above, since cyanobacteria sometimes propagates themselves in large quantities to kill a large number of fishes and shellfishes and pollute water, it has been a vital problem how to exterminate cyanobacteria to prevent water pollution.
In order to exterminate cyanobacteria, following methods have been implemented or proposed: (1) blowing ozone into water and making cyanobacteria contact to the ozone; (2) making water containing cyanobacteria pass a narrow passage that is enclosed by transparent glass plates or the like, and irradiating ultraviolet rays to the water passing the passage; (3) generating babbles in water to divide clustered cyanobacteria; (4) agitating water with an underwater fan or the like to divide clustered cyanobacteria; (5) absorbing cyanobacteria to zeolite and processing the cyanobacteria by plankton or the like; (6) absorbing cyanobacteria to charcoal and processing the cyanobacteria by plankton and so on.
With the methods (1) and (2), cells of cyanobacteria can be destroyed securely; on the other hand, it is dangerous and difficult to handle ozone and ultraviolet rays. In addition to the above, the quantity of cyanobacteria that can be exterminated is very small, so that it is impossible to catch up with the propagation of cyanobacteria. Further, other planktons also die. And, both initial and running costs of these methods are high.
The methods (3) and (4) have the advantage that an apparatus used for the methods is simple, however, these methods lack reliability of extermination of cyanobacteria. That is, there is a fear that nutriments for cyanobacteria are scraped out of the ground under the water and are agitated in the water, which promotes the propagation of the cyanobacteria.
Next, the methods (5) and (6) have the advantage that an apparatus used for the methods becomes simple and they contribute to environmental protection, however, the quantity of cyanobacteria that can be exterminated is small, which makes it difficult to catch up with the propagation of cyanobacteria. Especially, zeolite sinks near the bottom of the water, and a suction spout of charcoal is also positioned near the bottom of the water. On the contrary, since the cyanobacteria stay near the water surface, zeolite and charcoal do not absorb cyanobacteria very much.
The present invention has been made in consideration of the above-mentioned problems, and the object thereof is to provide a clustered creature exterminating method that can securely exterminate clustered creature such as cyanobacteria in large quantity.
To accomplish the above object, clustered creature exterminating method according to the present invention comprises the steps of: pressurizing a fluid containing a clustered creature; suddenly lowering the pressure applied to the fluid; and destroying a bonding in the clustered creature by a cavitation caused by the pressure drop to exterminate the clustered creature.
In the above method, a pump may pressurize the fluid, and the fluid can be injected from nozzles that are connected to the pump to suddenly lower the pressure applied to the fluid.
It is possible to add another step of colliding the fluid injected from the nozzles to an object, and the step of colliding the fluid injected from the nozzles to an object may be a step of colliding the fluids with each other, the fluids being injected from opposing nozzles with each other. The clustered creature can be cyanobacteria, and the above methods are to be utilized to exterminate cyanobacteria.
Further, it is possible to add the step of inflicting friction loss on the fluids injected from the nozzles with each other, and this step may be caused by the interaction between the fluids injected from the opposing nozzles.
When fluid containing a clustered creature such as cyanobacteria is pressurized by a pump or the like and is injected from nozzles to suddenly lower the pressure of the fluid, the fluid causes a cavitation, which allows the clustered creature to be subject to strong destroying force. As a result, the clustered creature is divided into small pieces to lose energy for maintaining life, leading to death.
Otherwise, when the fluid injected from the nozzles is collided to an object such as a plate, or the nozzles are arranged so as to closely oppose to one another to collide the fluids injected from the both nozzles with each other, physically strong force is applied to the clustered creature in the same manner as described above, and the clustered creature is divided into small pieces to lose energy for maintaining life. When the clustered creature is cyanobacteria and the cyanobacteria are divided into many small pieces, gas cysts in their cells are also destroyed. Thus the cyanobacteria lose the ability to rise, and sink to the bottom of the water, which prevents them from photosynthesizing, resulting in death of the cyanobacteria. In place of the collision, it is also possible to divide the cyanobacteria into small pieces by applying shearing force through friction loss, which is generated when the fluids injected from the plurality of nozzles are rubbed with each other.
With the present invention, continuous processing is possible by using a pump, and increasing the discharge quantity of the pump allows the quantity of fluid in the process to increase, so that a large amount of cyanobacteria can easily be exterminated. Further, the construction of the apparatus used for this method is simple; the mechanical efficiency of the apparatus is high; and clustered creature can be exterminated instantly through a single processing, resulting in very high efficiency of the exterminating system.